Arrangement for recording and reproducing sound



y 1941- G. E. M. CORIN 2,242,968

ARRANGEMENT FOR RECORDING AND REPRODUCING SOUND Filed 001;. 28, 1938 Patented May 20, 1941 iJNiTEB ARRANGEMENT FOR REUQRDING AND BEPRQDUCING SOUND Gunnar Erik Magnus Carin, Stockholm, Sweden Application October 28, 1938, Serial No. 237,385 In Sweden March 28, 1938 4 Claims.

This invention relates to an arrangement for optically recording and reproducing sound. Diiferent optical or photographic methods are used for producing a sound record on, for example, the sound track of a moving film. It has hitherto been common practice to obtain a record of either the varying area type or of the varying density type. By the varying density methods, for example the flashing lamp method or the Kerr cell method, the density of the sound track varies with the sound recorded thereon. Technical difficulties are, however, encountered in obtaining the correct development.

By the variable area methods, the variation of the area of the sound track corresponds to the variations of the sound. Such curves, which are easier developed, can for example be obtained by the mirror-oscillograph-method. By this method a mirror suspended on copper-wires or sil- Vere-d quartz-wires is vibrated when varying currents pass the wires. The recorded sound, however, gets a strong and decided metal-tone. This metallical tone is especially remarkable by producing piano and orchestra. The reproduced piano-music does not sound like piano but like something else for instance music on metallic bells and the reproduced orchestra-music has not the natural softness. Further is noted that by employing the methods just described a great amplifying of the current is required.

The object of the present invention is to avoid the said disadvantages and to efiect by simple means such a recording of the sound which makes a natural reproducing possible. This is obtained thereby that a current varying in accordance with the sound is arranged to actuate, for example on electro-dynamic or electro-magnetic way a supporting member manufactured of a flexible material being as dead or soundless as possible, said member carrying an object, for example a shutter, the movement of which can be photographically recorded on a record of the varying area type.

The invention will now be described with reference to the accompanying drawing. is a view showing diagrammatically the parts combined with a supporting member for the movable coil in an electro-dynamic soundrecorder. Figure 2 illustrates by Way of example the construction of a supporting member in accordance with the present invention. Figure 3 shows a modification of the supporting member.

In Figure 1 a magnet i is shown, for example a permanent magnet or an electro-magnet. A coil 2 is situated in the magnetic field above the Figure .l

magnet, which coil is fastened to the centre of the underside of a supporting member. The outer part of the supporting member is so fastened to a holder that the coil is at a suitable distance from the magnet. The member 3 carries an opaque object 4 for example a shutter, which is interposed into the path of a lightbeam. When the coil is fed with a varying current in known manner produced over a microphone and amplifiers, the coil tries to vibrate in the magnetic field in accordance with the variations of the current. If the supporting mem ber 3 is constructed in accordance with the invention, the coil and consequently the shutter 4 will vibrate up and down in a manner corresponding so much as possible to the current through the coil. A light-beam from a constant light-source directed approximately perpendicularly to the plan of the drawing against the shutter 4 will be blocked off in accordance with the variations of the current. The light-beam thereafter can be photographically recorded in known manner so that a sound track of variable area type is obtained.

In Figure 2 the supporting member 3 is shown seen from above. t is manufactured in the following way: an equilateral triangle is made of material, which is as far as possible soundless or dead and which has flexibility. From this triangle three sides or legs B are cut out as shown in Figure 2. Such a material can consist of canvas-Bakelite. If this is selected with a thickness of about 0.7 mm. the legs B can suitably be made 6.5 mm. wide and about 70 mm. long.

This triangle-shaped figure is secured with each one of its three ends by screws or riveting to a leg of an arrangement C, which seen from the side has a shape of a reversed V. The second leg of the arrangement C is for example riveted to a plate K, which can be moved backwards and forwards inside a casing E fastened to a holder A. This holder is placed on a fixed distance from the magnet. The V-shaped arrangements C are made of flexible, elastic material for example German silver sheet with, a thickness of 0.7 mm. The length of the legs is about 8 mm. The width of the arrangement C is chosen equal to the width of the material at the ends of the triangle-shaped figure, for example 10 mm.

There are a stopscrew D and a regulating screw F for each casing E and each corresponding plate. The elastic arrangements C act as springs which are adjustable by the regulating screws to give the supporting member the desired tension, by means of which the natural frequency can be chosen beyond the limit of the human ear. Thereafter the plates K are fastened with the stopscrews. Other arrangements than the proposed arrangement C might of course be used for giving the system the desired tension.

Down to the triangle-shaped figure B a triangle-shaped equilateral plate G is fastened. As shown in Figure 2 the angles of the plate G is thereby fastened to the center-point of the legs B. The coil 2, Figure 1, is fastened to the underside of the plate G as is shown with dashed lines I in Figure 2. The plate G is also made of flexible and as far as possible soundless material, for example paperor canvas-Bakelite. The thickness of the material can be chosen 0.8 mm.

The shutter 4 is fastened to the centre of the upper side of the plate. The central portion of the plate G is movable only axially with respect to the magnet. The supporting member is so constructed that it prevents other movement. The vibrations of the shutter 4 can be photographically recorded upon a continually moving strip of light-sensitive material by means of known optical systems.

By using the mentioned arrangements for recording sound the recorded sound will be free from metal tone and it gets natural timbre and clearness. It is to note that by recording according to the proposed method the sound from the different instruments of an orchestra will differ clearer than by other methods in use. The recorded sound seems to the ear as if the orchestra would be in the room.

By the example, shown on the drawing, the supporting member is used in an electro-dynamic system. The proposed supporting member of course also can be used in the same way in other electric systems bywhich a movable member is actuated by the current. The movable parts thereby are fastened in the centre of the triangular plate of the supporting member.

By the modification, shown in Figure 3, the triangle-shaped plate G, Figure 2, is replaced by a round plate, which practically forms an inscribed circle in the triangle-shaped figure B. The round inner-plate R can be cut out of the same plate as the figure B. This plate consists also of a soundless but flexible material for example canvas-Bakelite. Thereafter a round outcut is made in the plate R as shown in Figure 3. This modification is especially suitable for a supporting member which is to have less sensi tiveness than the arrangement according to Figure 2. The round inner-plate touches as shown in Figure 3 in three points the legs B. By decreasing or increasing the joint distance the sensitiveness of the supporting arrangement will be increased or decreased. The common jointdistance can for example be 5 mm. by a width of the part B of 5 mm.

The supporting arrangement used for the coil in electro-dynamic loudspeakers or for the armature of electro-magnetic loud-speakers can be replaced by the supporting members according to Figures 2 and 3. The coil or the armature thereby is placed in the centre of the innerplate of the supporting member. With these supporting arrangements the paper-cone of the loudspeakers works quickly, and the tones will be pure and clear. The armature and especially the coil works very regularly being surrounded by a uniform supporting member.

The supporting member according to Figure 3 which has the less sensitiveness has proved to be especially suitable for loud-speakers. When used for loud-speakers the tensioning means CDEFK shown in Figure 2 can be omitted and replaced by a direct fastening of the supporting member to the holder. The system is thereby given the correct tension by the manufacturing. The canvas-Bakelite is taken somewhat thinner in this case than for the supporting member for recording the sound. An especially suitable combination for recording and reproducing sound is eifected if the member according to Figure 2 is used to record and the member according to Figure 3 is used to reproduce the sound.

The excellent acoustic quality of the sound, recorded by the supporting member characterizes also the sound, reproduced by a loud-speaker with the above-mentioned supporting member for the coil.

I claim:

1. An arrangement for recording and reproducing sound including means for creating a magnetic field, a movable coil associated therewith, a supporting member for said movable coil, said member consisting of an inner and an outer part, both these parts being formed of a flexible material which is as dead or soundless as possible, said outer part consisting of three legs forming the sides in a triangle, tensioning means for securing the three ends of said triangleshaped outer part to a holder, said inner part being secured to the central points of the three legs of said outer part, a shutter carried by the center of said inner part, means for directing a light beam from a constant light-source perpendicularly to the movement of said shutter, and means for supplying a varying current to said movable coil, which is carried by said inner part, to move said shutter in accordance with the current.

2. An arrangement as claimed in claim 1, in which said inner part of the supporting member consists of a triangle-shaped plate, the angles of which are secured to the central points of the three legs forming the sides in the triangleshaped outer part.

3. An arrangement for sound-recording and reproducing, in which the sound on electric way is arranged to actuate a movable part, for said movable part a supporting member consisting of a round inner-plate and a triangle-shaped outerplate which plates are manufactured of Bakelite, said outer plate consisting of three legs forming the sides in a triangle, tensioning means for securing the three ends of said triangle-shaped outer plate to a holder, said inner plate being secured to the central points of the three legs of said outer part.

4. An arrangement as claimed in claim 3, in which said inner-plate is manufactured of paper- Bakelite and said outer-plate is maniifactured of canvas-Bakelite.

GUNNAR ERIK MAGNUS CORIN. 

